Growth Management Act. The Growth Management Act (GMA) is the comprehensive land use planning framework for counties and cities in Washington. The GMA establishes land-use designation and environmental protection requirements for all Washington counties and cities. The GMA also establishes a significantly wider array of planning duties for 28 counties, and the cities within those counties, that are obligated to satisfy all planning requirements of the GMA. These jurisdictions are sometimes said to be fully planning under the GMA.

The GMA also directs fully planning jurisdictions to adopt internally consistent comprehensive land use plans. Comprehensive plans are implemented through locally adopted development regulations and both the plans and the local regulations are subject to review and revision requirements prescribed in the GMA. Comprehensive plans must be reviewed and, if necessary, revised every ten years to ensure it complies with the GMA. When developing their comprehensive plans, counties and cities must consider various goals set forth in statute.

State Building Code. The State Building Code (SBC) provides a set of statewide standards and requirements related to building construction. The SBC is comprised of various international model codes (model codes), including building, residential, fire, and plumbing codes, adopted by reference by the Legislature. The model codes are promulgated by the International Code Council.

The State Building Code Council (SBCC) is responsible for adopting, amending, and maintaining the SBC. The SBCC must regularly review updated versions of the model codes and adopt a process for reviewing proposed statewide and local amendments.

Cities and counties may amend the SBC as applied within their jurisdiction, except that amendments may not be below minimum performance standards and no amendment affecting single or multifamily residential buildings may be effective until approved by the SBCC.

Middle Housing. In 2023, the Legislature passed E2SHB 1110, requiring certain cities planning under the GMA to authorize minimum development densities on lots zoned predominantly for residential use and defining provisions related to middle housing within six months of the city's next required comprehensive plan update.

A fully planning city with a population of at least 25,000 but less than 75,000 must include authorization for at least two units per lot, four units per lot within one-quarter mile walking distance of a major transit stop, and four units per lot if at least one unit is affordable housing. A fully planning city with a population of at least 75,000 must include authorization for at least four units per lot, six units per lot within one-quarter mile walking distance of a major transit stop, and six units per lot if at least two units are affordable housing.

A city must allow at least six of the nine types of middle housing and may allow accessory dwelling units (ADUs) to achieve the minimum density requirements. Middle housing is defined as buildings compatible in scale, form, and character with single-family houses and contain two or more attached, stacked, or clustered homes including duplexes, triplexes, fourplexes, fiveplexes, sixplexes, townhouses, stacked flats, courtyard apartments, and cottage housing. Cities are not required to allow ADUs or middle housing types beyond the density requirements.

Beginning six months after its next periodic comprehensive plan update, cities and counties fully planning under the GMA must allow co-living housing as a permitted use in any zone within an urban growth area that allows multifamily residential uses, including mixed use development.

A city or county subject to this act may not require co-living housing to:

• contain room dimensional standards larger than required by the state building code;
• provide a mix of unit sizes or number of bedrooms;
• include other uses;
• provide off-street parking within one-half mile walking distance of a major transit stop; and
• provide more than one-quarter off-street parking space per sleeping unit.

A city or county subject to this act may not:

• require any standards for co-living housing more restrictive than those required for other types of residential uses in the same zone;
• exclude co-living housing from participating in affordable housing incentive programs; and
• treat a sleeping unit in co-living housing as more than one-quarter of a dwelling unit for purposes of calculating dwelling unit density or fees for permitting and utility connection.

A city or county may only require a review, notice, or public meeting for co-living housing that is required for other types of residential uses in the same location, unless otherwise required by state law.

Any conflicting provisions in local development regulations after the deadline are superseded, preempted, and invalidated.